Many portable machines are driven hydraulically by hydraulic motors. Examples of machines which often are hydraulically driven are cutting machines with rotary cutting discs, circular saws, some types of boring machines, etc. A number of requirements are raised on those hydraulic motors which are used in this types of machines. They must not be too heavy and clumsy but instead be light and have a shape which is adapted to and which does not require a big space in or on that machine where they shall work. They shall be easy to operate, which i.a. implies that only quite a small power shall be needed for start and stop. They shall be comparatively cheap to manufacture, wherein it shall be observed that the machining of the motor body is responsible for a major part of the total costs. In order that the manufacture shall be as cheap as possible, the motor body therefore shall consist of only a few parts, at the same time as the design should be such that the number of rearrangements of the work-pieces for the machining operations shall be as small as possible. It is also desirable that there are as few places as possible in the motor body which have to be sealed in order to reduce the risks of leakage.
The above mentioned desired features have not been satisfied by today's technique.